The principal of a top Auckland school has issued a firm warning to students about "vicious" online bullying, saying they could be engaging in criminal behaviour

A video message was sent to parents of Epsom Girls Grammar School students late this week featuring a police officer who spelled out online bullying laws and the potential penalties for breaking them.

In the message to parents, principal Lorraine Pound said the content she'd seen can only be described as ugly and vicious.

Students have been warned they could be tracked if they break the law online.

The Ministry of Education's Katrina Casey says schools are increasingly involved in incidents where student activity at home or in their own time has an impact on their school life.